1. Technical Field
Embodiments of the present disclosure relate generally to delay locked loops (DLL), and more specifically to a fast-locking delay locked loop.
2. Related Art
A delay locked loop (DLL) is a closed-loop feedback circuit that adjusts the phase of its output to achieve a desired phase difference between the output and an input signal. The adjustment is typically done based on an error signal generated as a comparison result of the phases of the output and the input signal. The input signal and the output are typically clock signals.
The lock-time of a DLL is generally the time required for the output of the DLL to ‘lock to’ the input signal. Thus, for example, assuming the input signal is a clock, the lock-time is the time taken for the output of the DLL to be adjusted to have the desired phase difference from the phase of the input clock. The lock-time of a DLL may be expressed conveniently in terms of the number of clock cycles of an input clock.
It may generally be desirable that the lock-time of a DLL be short. For example, a clock data recovery (CDR) application may require an output clock of a DLL to be aligned with bit-boundaries of a serial data stream quickly (e.g., within an interval of the first few bit transitions representing a synchronization sequence transmitted at the beginning of the data stream), the output clock then being used to sample the data stream to recover the subsequent data bits.